On September 3, the Chinese capital will witness a massive military parade. The parade will become the highest point of the lavish celebrations, commemorating the 70th anniversary of the end of the Second World War in Asia.

Chinese diplomats worked hard to ensure that as many foreign dignitaries as possible would attend the celebrations. Admittedly, their success was limited: Most developed nations chose to send only low-level delegations to Beijing.

However, one feature on the list of attendees attracted much attention: while South Korea's President Park Geun-hye will be in Beijing on that remarkable day, her North Korean counterpart, Supreme Leader and First Chairman Kim Jong-un will not show up and will send one of his emissaries instead.

At first glance, this picture looks strange - even bizarre. Both Park and Kim hail from powerful political families, and both of them are scions of former leaders.

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However, in the days of the Second World War, Park's father was a young officer in the Imperial Japanese Army, whose defeat is now being celebrated in Beijing.

Kim's grandfather was a brave guerrilla commander in the war, waging a campaign against Japan.

Fraternal communist nation

Furthermore, North Korea is still technically China's ally, and - if official rhetoric is to be believed - a fraternal communist nation: one of few such nations to have survived to present day.

South Korea, on the other hand, is a liberal democracy and an ally of the United States. It even maintains some anti-communist legislation, which is widely ignored in practise.

However, there is nothing surprising about the presence of Park and the absence of her North Korean counterpart. Of course, a significant factor is Kim's notorious aversion to summits, but there are deeper reasons behind his absence in the Beijing celebrations.

The economy is what matters most in South Korea, and for the sake of the economy alone, Seoul works hard to improve relations with China.

The historical legacies and ideological commitments are frequently invoked in East Asia when it is necessary to justify policies, but in practise, economic interests and geostrategic calculations reign supreme.

South Korea is a liberal democracy, but China is still its largest trade partner. In recent years, South Korea's trade with China has exceeded its combined trade with Japan and the US, which are its second and third largest trade partners. The economy is what matters most in South Korea - and for the sake of the economy alone, Seoul works hard to improve relations with China.

It also helps that unlike many of China's neighbours, South Korea does not have a tradition of wars and hostility with China and has no problem with its fast political ascent. Despite being a US ally, South Korea does not want to be sucked into Sino-American clashes over territorial claims and other issues, which mean little to the average South Korean.

Lastly, in Seoul, there are growing doubts about the US' ability to remain the guarantor of South Korea's security in the long run.

Nuanced attitude

China is looking at these changes in Seoul's attitudes favourably. Unlike Japan, which is perceived in Beijing as the US' "unsinkable air carrier", the attitude towards South Korea is far more nuanced. Many Chinese analysts quietly hope that one day South Korea will completely drift away from the US.

On the other hand, the attitude towards North Korea in Beijing is remarkably harsh. Kim's state is widely seen as a troublesome, irresponsible and capricious neighbour - always demanding aid and concessions while ignoring China's vital interests.

South Korean President Park Geun-hye meets with Chinese President Xi Jinping in Beijing [REUTERS]

The North Korean nuclear programme threatens the non-proliferation agreement, which China - like all other "legally accepted" nuclear powers - is eager to maintain.

The North Korean brinkmanship threatens not only the stability along the Chinese borders, but it also creates a pretext for the US to maintain and increase their military presence in the region.

The Chinese are driven mad by North Korea's unwillingness to improve its economy through emulating Chinese market-oriented reforms.

In short, for the Chinese, North Korea is not attractive - unlike South Korea, with its sophisticated culture, huge market and willingness to make deals with Beijing.

Preferential trade conditions

However, these negative feelings are fully reciprocated in Pyongyang. North Korean leaders have always been eager to manipulate China in order to receive aid or preferential trade conditions, but they have never trusted their great neighbour. To an extent, this mistrust reflects a strong sense of nationalism that's common in the North, but it also reflects the sad experience of occasional Chinese interventions.

Finally, the Chinese want a reforming and non-nuclear North Korea, and this is exactly the option Kim and his advisers see as completely unacceptable. Rightly so or not, they believe that such a North Korea that China dreams of will not survive for long without being overwhelmed by both internal and external threats.

In the past, China was interested in supporting North Korea as a buffer zone. Such ideas are still widespread among Chinese officials and analysts, but many now doubt whether such a buffer zone is as important as it once was - after all, South Korea is slowly but surely changing in ways that China can only approve of.

Thus, regardless of official rhetoric, and irrespective of which side the current leaders' fathers and grandfathers fought for 75 years ago, the logic of the situation pushes South Korea towards better relations with China. But this same logic means that it makes more sense for North Korea to keep a certain distance from Beijing.

Andrei Lankov is a professor of Korean Studies at Kookmin University, Seoul. He is the author of "The Real North Korea: Life and Politics in the Failed Stalinist Utopia".

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.